Helium ion microscopy (HIM) is being used both to create and to inspect nanostructures for photonic and plasmonic devices. As part of a program exploring photoelectrons as sources for multiple beam electron beam lithography, fractal apertures are being developed to generate a sub-20nm light source using surface plasmon resonance. The fabrication was carried out by direct write helium ion milling into a 90 nm thick aluminum film deposited by evaporation onto a fused silica substrate. A machining …